Auto manufacturers are investigating radar, lidar, and vision-based pre-crash sensing systems to improve occupant safety. Pre-crash sensing systems have been recognized to have the potential of improving occupant safety by deploying the passive restraints devices earlier in a crash, or even before the actual impact. This extra time allows more flexibility for component design and can allow the passive restraints system to be individually tailored to the occupant and crash scenario.
Current vehicles typically employ accelerometers that measure decelerations acting on the vehicle body in the event of a crash. In response to accelerometers, airbags or other safety devices are deployed. The pre-crash sensors also sense information before impact concerning the size and closing velocity of the object, which cannot be calculated by conventional accelerometer-based sensors until after the crash. In certain crash situations it would be desirable to provide information before forces actually act upon the vehicle when a collision is unavoidable. The pre-crash sensing systems that exist today are significantly more complex than the accelerometer based systems, both in hardware and algorithm complexity.
Remote sensing systems using radar, lidar or vision based technologies for adaptive cruise control, collision avoidance and collision warning applications are known. These systems have characteristic requirements for avoiding false alarms. Generally, the remote sensing system reliability requirements for pre-crash sensing for automotive safety related systems are more stringent than those for comfort and convenience features, such as, adaptive cruise control. The reliability requirements even for safety related features vary significantly, depending upon the safety countermeasure under consideration. For example, tolerance towards undesirable activations may be higher for activating motorized seatbelt pretensioners than for functions such as vehicle suspension height adjustments. Non-reversible safety countermeasures, including airbags, require extremely reliable sensing systems for pre-crash activation.
Traditional pre-crash sensors such as radar, vision and laser systems are not capable of sensing the mass or stiffness of an object, which help define the collision severity of the crash event. Redundant sensors are necessary in order to achieve long-range target tracking, while also providing accurate short-range information about an impact-imminent target. Furthermore, the algorithms that have been developed to detect objects and imminent collisions are required to meet very high reliability targets for deploying non-reversible passive restraints devices (e.g. airbags). Given the complexity of the pre-crash sensing signal, along with the required fusion of targets from multiple sensors, often employing different technologies for sensing, such high reliability has not yet been achieved. Thus, to date, all applications of pre-crash sensing to restraints have been limited to either pre-arming of non-reversible restraints (e.g. airbags), or deploying of reversible restraint devices (e.g. electromechanical seatbelt pretensioners).
It would therefore be desirable to provide a pre-crash sensing system that provides accurate determinations as to the presence of a potential collision target. It would also be desirable to provide a system that takes into consideration the stiffness of the object detected.